Although the prior art has contemplated literally hundreds of various designs for bags and bag dispensing systems, relatively few have proved easily implemented and few yet have proved consistent in performance.
A list of prior patents which may be of interest is presented below
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 5,335,788 Beasley et al August 09, 1994 5,123,145 Huang et al May 25, 1993 5,183,158 Boyd et al Feb 02, 1993 5,014,852 Herrington et al May 14, 1991 5,013,290 DeMatteis May 07, 1991 4,989,732 Smith Feb 05, 1991 4,676,378 Baxley et al Jun 30, 1987 4,562,925 Pistner Jan 07, 1986 3,869,065 Wang Mar 04, 1975 ______________________________________
U.S. Pat. Nos. 4,989,732 and 5,183,158 to Mobil Oil Corporation teaches a self opening bag system wherein there is contemplated a thermoplastic bag pack having handles emanating from opposing sides of a bag mouth, wherein there is provided a pressure bonded area of the pack, such that the plastic film of the bags are in "face to face" engagement between the top and base of the handles, and beneath the medial area of the bag mouth.
The Mobil patents are distinguishable from the present invention, as they contemplate a non-permeating engagement of the film in the various layers of plastic forming the bag pack. Further, unlike the Mobil patents, the present invention does not require pressure-bonding below the mouth of the bags, as is specifically contemplated, and believed required, for the Mobil system to work.
Unlike Mobil, the present systems punch configuration for providing a permeated, releasible pressure bond provides sufficient releasable binding of the film layers, via melding of the severed film, to draw the next bag open for dispensing, with the removal of the full bag from the rack, without the necessity of the medial pressure bond below the bag mouth as in '732, as well as a separate pressure bond at the base of the bag and pack, as contemplated and claimed in '158.
U.S. Pat. No. 5,013,290 to DeMatteis contemplates a t-shirt bag pack formed of co-extruded plastic film, wherein the inner layer comprises a relatively low friction coefficient, the outer layer comprises a generally high friction coefficient, said t-shirt bag pack having formed in the handles a handle aperture having a flap designed to rest upon the rods of a dispenser rack in such a manner such that the flaps are oriented so that they are disposed away from the mass of the bags to pass the weight of the bag pack of said bundle downward through the flaps and onto said rods. The patent refers to the high friction, outer layer of the co-extrusion being formed of low density polyethylene resin (LDPE), the inner layer formed of high density polyethylene resin (HDPE).
U.S. Pat. No. 5,335,788 to Sonoco Products Company teaches a "Self-Opening Polyethylene Bag Stack and Process for Producing Same", teaching a mono-extruded bag formed from HDPE film, said film having a corona treatment applied thereto. Quoting this patent (Col 1, Ln 67-Col2 Ln45):
"In general, the phenomenon of corona-induced self-adhesion of polyethylene film is not a new development as far as film processors are concerned. On the contrary, processors continually fought this problem, more commonly known as "blocking" for many years. In fact, most LDPE and LLDPE contain specific amounts of slip and anti-block additives to counteract the "blocking" effect. However, high molecular weight, high density polyethylene (HDPE) which has substantially greater crystallinity and is a more substantially linear polymer does not tend to block, and is more often than not does not contain any slip or antiblock additives.
The mechanism of hydrogen bonding in polyethylene films a result of corona treating is reported by Owens in J. Appl. Polym. Sci. 19, 256-271 (1975). The polyethylene films treated by Owens were LLDPE (the material was reported to have a density of 0.926). However, the conditions of heat and pressure which readily caused blocking in corona treated LDPE and LLDPE seem to have little or no effect on HDPE. PA1 Accordingly, although easy-open bag stacks of LLDPE and LDPE film bags can be readily provided without the necessity of a separate adhesive layer between the bags, a separate adhesive layer is still required between HDPE bags when these bags are prepared by prior art manufacturing process. Moreover, with low density polyethylene materials, the known process for forming self-opening bags such as described in U.S. Pat. No. 5,087,234 to Prader to not allow for substantial adjustment of the degree of bonding between adjacent bags or variation of bonding locations."
Apparently for similar reasons, although the process disclosed in Prader U.S. Pat. No. 5,087,234 can be successfully employed on low density polyethylene materials to form self-opening bag stacks, this process is generally ineffective when used for high molecular weight, high density polyethylene (HDPE) bag stacks. Thus, this process is not successful even when the degree of corona discharge treatment is applied to the surfaces of the tubular film is increased in order to induce self-adhesion of the outer surfaces of adjacent bags during the mouth and handle cutting process. Similarly, even when the cutting blade edges are dulled in order to increase the degree of pressure exerted on the bags during the cutting process, self-adhesion of adjacent bags for self opening is not achieved with HDPE.
Unlike the present invention, the '788 patent not only appears to contemplate a film of at least 50% HDPE in the compression area, but also teaches a compression means utilizing a blunt end punch, wherein the compressed film is not severed, the blunt punch apparently compressing the bag walls together resulting in decreased thickness. Further, the above quote teaches that the novelty '788 rests in the ability to corona treat and punch HDPE bags in order to provide an HDPE bag stack having self-opening characteristics, the quote apparently indicating that corona treating LDPE is not particularly new. Unlike '788, the present invention contemplates a system utilizing co-extruded film, wherein the outer layer comprises mostly, if not all, LDPE or LLDPE product. Further '788 does not contemplate the utilization of a punch formed of a multi-faceted cutting blades, as is shown and claimed in the present invention, which punch penetrates and severs the bag walls, melding the cut edges together, as opposed to compressing them together, as is taught in '788.